1. Field of the Invention
This invention relates to aqueous dispersions of crystalline polymers, methods for making such dispersions and the use of such dispersions for coating substrates.
It is known to use certain organic polymers to provide coatings on a wide variety of substrates, including hair (see U.S. Pat. Nos. 4,196,190; 4,452,216; 4,834,968 and 4,983,383); fabrics (see U.S. Pat. Nos. 3,644,241; 3,833,393 and 4,780,499); and seeds and other organisms (see U.S. Pat. No. 5,129,180). It is also known to set a fabric by impregnating the fabric with a monomer component, and polymerizing the monomer while maintaining the fabric in a desired configuration (see U.S. Pat. No. 4,401,688).
One class of polymers which has been used for coating substrates comprises side-chain crystalline (xe2x80x9cSCCxe2x80x9d) polymers. However, the known coating compositions containing SCC polymers have the disadvantage that the polymer is dissolved in an organic solvent. Organic solvents are expensive, require environmental controls, and are particularly undesirable for application to human hair or to an organism.
Attempts have been made to prepare aqueous dispersions of SCC polymers (see British Polymer Journal 20, 521-524 (1988), U.S. Pat. Nos. 5,506,307 and 5,516,865, and Japanese Patent Document No. 6-192341), but the results have been poor and/or the techniques expensive.
We have discovered, in accordance with the present invention, that very valuable results can be achieved by coating substrates with aqueous dispersions of polymeric particles in which the polymer is a crystalline polymer containing units derived from at least one hydrophobic monomer and preferably also from a lesser amount of units derived from at least one hydrophilic monomer. Particularly useful results are obtained when the substrate is a seed or other organism, or a fibrous material. We have also discovered, in accordance with the invention, novel aqueous dispersions of crystalline polymers and methods of making such dispersions.
In one of its embodiments, this invention provides a substrate having a solid polymeric coating thereon, the coating having been obtained by:
(1) applying to the substrate an aqueous dispersion of solid particles comprising a crystalline polymer, the polymer (a) having a melting point Tm and (b) comprising units derived from a hydrophobic monomer, and
(2) evaporating water from the dispersion to form the solid polymeric coating;
the coating having at least one of the following characteristics:
(A) at temperatures below Tm, the coating is substantially impermeable to water (as hereinafter defined), and at temperatures above Tm, the coating is substantially permeable to water (as hereinafter defined);
(B) the polymer is a crosslinked polymer having a gel content of at least 50%,
(C) the polymer is derived from a monomer component comprising:
(i) a hydrophobic monomer component comprising a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point Tc, and
(ii) a hydrophilic monomer component comprising a hydrophilic monomer, the ratio by weight of the hydrophobic monomer component to the hydrophilic monomer component being 10:1 to 50:1;
(D) the polymer is derived from a monomer component comprising a hydrophobic monomer component comprising (i) a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point Tc, and (ii) a second hydrophobic monomer which
(a) is such that a homopolymer thereof is amorphous and has a glass transition point Tg which is less than Tc, and
(b) is present in amount such that Tm is (Tcxe2x88x925)xc2x0 C. or less;
(E) the polymer is derived from a monomer component comprising a hydrophobic monomer component comprising (i) a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point Tc, and (ii) a second hydrophobic monomer which
(a) is such that a homopolymer thereof is amorphous and has a glass transition point Tg which is more than Tc, and
(b) is present in amount such that the coating has a tack at (Tc+10)xc2x0 C. which is less than the tack at (Tc+10)xc2x0 C. of a coating formed under the same conditions from a composition which is identical except that the crystalline polymer does not contain units derived from the second hydrophobic monomer;
(F) the polymer is derived from a monomer component comprising:
(i) a hydrophobic monomer component comprising a hydrophobic monomer, the hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point Tc;
(ii) a hydrophilic monomer component comprising a hydrophilic monomer; and
(iii) a crosslinking monomer having at least two polymerizable groups;
(G) the polymer is derived from a monomer component comprising one or more monomers containing carboxyl groups, at least 75% of the carboxyl groups having been neutralized;
(H) the polymer is crosslinked by an external crosslinker (as herinafter defined);
(I) the particles of the dispersion have coalesced to form a continuous coating, but retain a particulate character;
(J) the coating contains less than 1% of unreacted monomer, based on the weight of the polymer; and
(K) at least some of the particles comprise a core comprising said crystalline polymer and a coating around the core comprising a substantially amorphous polymer.
In describing the invention below, unless otherwise noted, parts, percentages and ratios are by weight. The monomers from which the crystalline polymer is derived are important. The term hydrophobic monomer is used herein to denote a monomer whose solubility in water at 25xc2x0 C. is less than 2%. The term hydrophilic monomer is used herein to denote a monomer whose solubility in water at 25xc2x0 is 2% or more. More than one hydrophobic monomer can be used, and the term hydrophobic monomer component is used herein to denote all the hydrophobic monomers collectively, and is often abbreviated herein to xe2x80x9cBMC.xe2x80x9d More than one hydrophilic monomer component can be used, and the term hydrophilic monomer component is used herein to denote all the hydrophilic monomers collectively, and is often abbreviated herein to xe2x80x9cPMC.xe2x80x9d The monomers from which the crystalline polymer is derived can include one or more monomers which contain two or more polymerizable groups, so that the polymer is crosslinked. Such monomers (which may be hydrophobic or hydrophilic) are referred to herein as crosslinking monomers; and the term crosslinking monomer component is used herein to denote all the crosslinking monomers collectively, and is often abbreviated herein to xe2x80x9cXLC.xe2x80x9d Except where otherwise noted, percentages of monomers given herein (both as starting materials, and as residual monomers) are based on the total weight of the monomer starting material. As further discussed below, the monomers used in preparing the crystalline polymers are preferably n-alkyl acrylates or methacrylates. The abbreviation CnA and ""CnMA are used to denote n-alkyl acrylates and n-alkyl methacrylates, respectively, in which the n-alkyl group contains x carbon atoms. For example C4A denotes butyl acrylate, and C12MA denotes lauryl methacrylate.
Crystalline melting points given herein (Tm and Tc) are the peak of a curve produced using a differential scanning calorimeter (DSC) at a heating rate of 10xc2x0 C. per minute, and using the second heat cycle. The onset of melting (To) is taken from the same curve. To, Tm and Tc are measured in the conventional way well known to those skilled in the art. Thus Tm and Tc are the temperature at the peak of the DSC curve, and To is the temperature at the intersection of the baseline of the DSC peak and the onset line, the onset line being defined as the tangent to the steepest part of the DSC curve below the peak. Tack values given herein are measured as follows. The latex is applied to a polymeric film (a polyester film available from DuPont under the trade name xe2x80x9cMylar,xe2x80x9d or a filled polyolefin film available from PPG under the trade name xe2x80x9cTeslinxe2x80x9d), at a rate such that after the coating has been dried at 65xc2x0 C. for 2 hours, it has a thickness of about 30 microns. Two such films are laminated together at 35xc2x0 C. and the tack is measured with a vslip/peel tester at 230 cm/min.
In a first preferred aspect, this invention provides a method of treating an organism to extend its dormancy, the method comprising (1) applying to the organism a non-phytotoxic coating composition which comprises (a) water, and (b) suspended in the water, particles which comprise a crystalline polymer having a melting point Tm of 0xc2x0 to 40xc2x0 C.; and (2) causing water to evaporate from the composition, thereby forming on the organism a coating which (a) at temperatures below Tm is substantially impermeable to water and (b) at temperatures above Tm is substantially permeable to water.
In a second preferred aspect, this invention provides a composition which comprises:
(a) water,
(b) suspended in the water, particles comprising a crosslinked crystalline polymer which
(i) has a gel content of at least 50%,
(ii) contains less than 1% of unreacted monomer, and
(iii) is derived from a monomer component comprising:
1) a hydrophobic monomer component comprising a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point Tc, and
2) a hydrophilic monomer component comprising a hydrophilic monomer, and
3) a crosslinking monomer having at least two polymerizable groups; and
(c) a surfactant.
In a third preferred aspect, this invention provides a method of making a composition in accordance with the second preferred aspect, the method comprising:
(a) providing an aqueous reaction medium comprising:
(i) water,
(ii) the monomer component, the monomer component containing at least 2% of the hydrophilic monomer component,
(iii) the surfactant, and
(iv) at least 1% based on the water, of a cosolvent which increases the solubility of the hydrophobic monomer component in the water;
(b) polymerizing the monomer component in the aqueous reaction medium so that at least 99% thereof polymerizes to form the crystalline polymer in the form of particles having an average particle size less than 0.5 microns, the monomer component being present in amount such that at the end of the polymerization, the solid polymer content of the reaction mixture is at least 30%; and
(i) the surfactant being present in amount such that the monomer component is initially present in the aqueous reaction medium in the form of droplets having a diameter greater than 10 microns, and/or
(ii) the surfactant and the cosolvent being present in amount such that the hydrophilic monomer component is substantially randomly polymerized in the crystalline copolymer.
In a fourth preferred aspect, this invention provides a method for preparing an aqueous suspension, the method comprising the steps of:
(a) providing an aqueous reaction medium comprising:
(i) water,
(ii) a first monomer component comprising a hydrophobic monomer component comprising a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline, and
(iii) a surfactant;
b) polymerizing the first monomer component to form a crystalline polymer in the form of particles suspended in the reaction mixture; and
c) polymerizing a second monomer component to form a shell on said particles,
the amounts of said first and second monomer components being such that the product of step (c) has a solids content of at least 30%, and
the amount of surfactant being such that the product of step (c) contains particles having an average particle size of less than 0.5 microns and a residual monomer content of less than 1%.
In a fifth preferred aspect, this invention provides a composition suitable for use in setting a fibrous material, the composition comprising:
(a) water;
(b) particles suspended in the water, the particles comprising a crystalline polymer; and
c) an effective amount of an additive having a desired effect on the fibrous material. The term xe2x80x9ceffective amountxe2x80x9d is used herein to denote an amount which is sufficient to provide the fibrous material with desired benefits, taking into consideration the thickness, density, length and texture of the fibers.
In a sixth preferred aspect, this invention provides a method of coating a fibrous material, the method comprising:
(1) applying to the fibrous material a composition in accordance with the fifth aspect of the invention; and
(2) evaporating the water from the composition while the composition is in contact with the fibrous material, thereby forming a coating on the fibrous material.
This method can further comprise:
(3) while the coating is at a temperature above Tm, setting the fibrous material into a first desired configuration; and
(4) cooling the coating to below Tm while maintaining the fibrous material in the first desired configuration.
If desired, the method can further comprise:
(5) reheating the coating to a temperature greater than Tm;
(6) after reheating the coating, and while the coating is at a temperature above Tm, setting the fibrous material into a second desired configuration which is the same as or different from the first desired configuration; and
(7) cooling the coating while maintaining the fibrous material in the second desired configuration.
The term xe2x80x9ccooling the coatingxe2x80x9d includes merely leaving the coated material to cool in the ambient atmosphere, as well as methods in which active steps are taken to effect cooling. Fibrous materials which can be used include hair, particularly human hair, and woven, knitted and non-woven fabrics and other textile products such as grains, including cotton and cotton/polyester blend materials.
It is to be understood that in the foregoing description of the invention, and in the more detailed description set forth below, the various features which are disclosed may be used in any appropriate combination, and features which are disclosed in connection with a particular embodiment can be used singly or in combination in connection with the invention in general and in connection with other embodiments, except of course where the features are mutually exclusive.
A. Materials for Use In The Preparation of the Polymeric Dispersions
In order to prepare the aqueous polymeric dispersions which form part of the present invention, and/or which can be used to coat substrates in accordance with the invention, a monomer component is dispersed in water with the aid of a surfactant and preferably a cosolvent; optionally other additives may also be present. The reaction mixture is then subjected to conditions which cause the monomer(s) to react to form a polymer which remains in suspension in the reaction medium. The monomer component comprises a hydrophobic monomer component (BMC) and preferably also a hydrophilic monomer component (LMC). Either the BMC or the LMC, or both, can include a crosslinking monomer. The reaction mixture can also contain a crosslinking agent, which can be (a) a crosslinking monomer component (XLC) which comprises at least one monomer containing at least two polymerizable groups, or (b) an xe2x80x9cexternal crosslinker.xe2x80x9d An external crosslinker is a compound which increases the apparent molecular weight of the polymer without becoming a covalently bound part of the polymer, and which increases the mechanical strength of coatings formed from the aqueous dispersion of the polymer.
1. Monomer Components
(a) Hydrophobic Monomer Component (BMC)
The BMC comprises at least one first hydrophobic monomer such that a homopolymer thereof is crystalline and has a melting point Tc. It may also be desirable for the BMC to include at least one second hydrophobic monomer such that a homopolymer thereof is amorphous and has a glass transition point Tg. In one embodiment, Tg is less than Tc and the second hydrophobic monomer is present in amount such that the Tm of the polymer is (Tcxe2x88x925)xc2x0 C. or less. In another embodiment, Tg is more than Tc, in which case the amount of the second hydrophobic monomer is preferably such that a coating formed from the composition has a tack at (Tc+10)xc2x0 C. which is less than the tack at (Tc+10)xc2x0 C. of a coating formed under the same conditions from a composition which is identical except that the crystalline polymer does not contain units derived from the second hydrophobic monomer. The amount of the second hydrophobic monomer is generally less than 50%, preferably 5 to 40%, particularly 5 to 30%, based on the BMC.
Preferred hydrophobic monomers are xcex1, xcex2-ethylenically-unsaturated monomers, particularly n-alkyl acrylates and n-alkyl methacrylates in which the n-alkyl groups contains 4 to 24 carbons.
Preferred first hydrophobic monomers are monomers whose homopolymers are side chain crystalline (SCC) polymers. SCC polymers are well known, and are described for example in the following publications, to which reference should be made for a more complete disclosure of first hydrophobic monomers suitable for use in this invention: J. Poly. Sci. 60, 19 (1962), J. Poly. Sci. (Polymer Chemistry) 7, 3053 (1969), 9, 1835, 3349, 3351, 3367, 10, 1657, 3347, 18, 2197, 19, 1871, J. Poly. Sci., Poly Physics Ed 18 2197 (1980), J. Poly. Sci. Macromol. Rev. 8, 117 (1974), Macromolecules 12, 94 (1979), 13, 12, 15, 18, 2141, 19, 611, JACS 75, 3326 (1953), 76, 6280, Polymer J 17, 991 (1985), Poly. Sci USSR 21, 241 (1979), U.S. Pat. Nos. 4,380,855, 5,120,349, 5,129,180, 5,156,411, 5,254,354, 5,387,450, 5,412,035, 5,469,869, and 5,665,822. Particularly preferred first hydrophobic monomers are those which result in SCC polymers in which the side chain comprises a linear polymethylene group containing 12 to 50, preferably 14 to 22, carbons, or a linear perfluorinated or substantially perfluorinated polymethylene group containing 6 to 50 carbons. Mixtures of such hydrophobic monomers can be used. Preferred monomers are those which are commercially available, in particular the n-alkyl acrylates. Preferred first hydrophobic monomers for use in the invention comprise at least one of C12MA, C12A, C14A, C14MA, C16A, C16M, C18A, mixtures of C18A, C20A and C22A, mixtures of C26A and C40A, fluorinated C8A, and mixtures of fluorinated C8A, C10A and C12A, and other monomers which produce substantially the same final polymers, e.g. acrylamides and methacrylamides.
Preferred second hydrophobic monomers are monomers whose homopolymers have a Tg of xe2x88x9250 to 120xc2x0 C., for example n-butyl, isobutyl, and tertiary butyl methacrylates, vinyl acetate, vinyl propionate, n-butyl and t-butyl acrylates, homopolymers of which have TgS of 32, 65, 107, 28, 10, 40, and 52xc2x0 C., respectively. Examples of suitable second hydrophobic monomers are linear and branched chain alkyl, hydroxyalkyl and alkoxyalkyl acrylates, methacrylates, acrylamides, and methacrylamides, and vinyl esters, in particular C8A, C8MA, 2-ethylhexyl acrylate and methacrylate, C6A, C6MA, C4A, C4MA and mixtures thereof.
(b) Hydrophilic Monomer Component (LMC)
The LMC comprises at least one hydrophilic monomer and is preferably present in an amount of 2 to 10%, particularly 2 to 5%. The hydrophilic monomer is preferably an xcex1xcex2-ethylenically unsaturated monomer, for example a vinylic compound such as acrylic acid; methacrylic acid; an alkyl, hydroxyalkyl or alkoxyalkyl acrylate or methacrylate (e.g. hydroxy ethyl methacrylate); acrylamide and methacrylamide; acrylic or methacrylic acid; acrylamide; methacrylamide; maleic anhydride; itaconic acid; a comonomer containing an amine group; and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and combinations thereof. Preferably the hydrophilic monomer is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, 2-acrylamido-2-methylpropane sulfonic acid, acrylamide, methacrylamide, or hydroxyethyl (meth)acrylate or a mixture thereof.
(c) Crosslinking Monomer Component (XMC)
The XMC, if present, comprises at least one crosslinking monomer which contains at least two polymerizable groups, e.g. vinylic groups. The XMC is preferably used in amount such that the polymer has a gel content of at least 50%, particularly at least 60%, up to substantially 100%. Preferred hydrophobic crosslinking monomers include 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,14-tetradecyidiol diacrylate, divinyl benzene, vinyl crotonate, divinyl ether, and 1,3,5-triallyl triazine trione, and mixtures thereof. Preferred hydrophilic crosslinking monomers include ethylene glycol diacrylate, and ethylene glycol dimethacrylate, and mixtures thereof.
The amount of crosslinking monomer is preferably such that the polymer has a crosslink density (number of crosslinks per weight average molecular weight) of at least 0.01, preferably at least 0.05, particularly at least 0.1, so that the polymer resists flow above Tm. A high gel content (e.g. crosslinking beyond 1 to 10 mole percent) is not generally needed and can result in decreased crystallinity and poor performance. The crosslinked polymer preferably has a heat of fusion of at least 10, preferably at least 20, J/g.
The use of an XMC is important when it is desirable for the coating to be easily removed, because the resulting crosslinked polymer particles are harder; and when water is evaporated from dispersion, the particles do not easily diffuse into each other. The resulting coatings have a particulate character and as a result are more easily removable and frangible. This is particularly important for hair-setting compositions, since it is desirable that the film-forming material be removable by washing hair with water. It is also particularly important for seed coatings; prior art non-particulate coatings can remain on the seed and inhibit seed germination. In the absence of crosslinking, when the water is evaporated, the latex particles are brought together by capillary action, and the water is squeezed out from the interstitial spaces. The particles coalesce and lose their identity, and a substantially uniform film results.
(d) Carboxyl-Containing Monomer Component
The monomer component can contain one or more monomers containing carboxyl groups, the carboxyl groups being partially, preferably at least 75%, neutralized (e.g. with NaHCO3) after the polymerization is complete.
(e) Preferred Monomer Components
Preferred monomer components result in a crystalline polymer having a sharp melting point, preferably such that (Tmxe2x88x92To) is less than 20xc2x0 C., preferably less than 15xc2x0 C., particularly less than 10xc2x0 C., where To is the onset of melting on the DSC curve. Particularly preferred monomer components comprise:
(i) 50 to 100%, preferably 65 to 95%, of at least one first hydrophobic monomer which is an alkyl acrylate, alkyl methacrylate, alkyl acrylamide, alkyl methacrylamide, alkyl vinyl ether or alkyl vinyl ester in which the alkyl group is an n-alkyl group containing 12 to 50 carbon atoms;
(ii) 0 to 35% of at least one second hydrophobic monomer which is an alkyl acrylate, alkyl methacrylate, N-alkyl acrylamide, alkyl vinyl ether, or alkyl vinyl ester in which the alkyl group is an n-alkyl group containing 4 to 12 carbon atoms; and
(iii) at least 2%, and preferably no more than 10% of at least one hydrophilic monomer which is acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, hydroxyethyl acrylate or methacrylate itaconic acid, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, a tetraalkylammonium acrylate, vinyl acetate or N-vinyl pyrrolidone.
2. External Crosslinkers
External crosslinkers, when used, are generally compounds containing charged groups which interact with charged groups in the polymer. Preferred external crosslinkers contain metal (e.g. Mg, Mn, Zn, Ca, Ti or Zr) cations or bidentate or multidentate amine groups. Other external crosslinkers are non-metallic and organic compounds, e.g. triethylene tetramine, ethylene diamine, diethyl aminopropylamine and bis(quaternary ammonium) salts. The amount of external crosslinker is generally 0.1 to 10, preferably 0.5 to 3%, based on the monomer component. Some external crosslinkers do not have any effect until a coating is prepared from the dispersion. For example, the cation can be present as an ammonia complex and not become effective until the ammonia is removed during the evaporation step. Thus, an aqueous solution containing Zn(NH3)++ ions can be used in this way.
External crosslinkers can be used in combination with crosslinking monomers.
3. Surfactants
The reaction medium for the polymerization comprises at least one surfactant, preferably at least one ionic surfactant and at least one non-ionic surfactant, to suspend and stabilize the particles formed by polymerizing the monomer component in the aqueous reaction medium. The amount of surfactant can be 0.8 to 10%, preferably 1 to 5%, based on the reaction medium. However, the optimum amount of surfactant depends also on the amount of cosolvent present, as further described below. Preferably, sufficient surfactant is present to enable the monomer component to be present initially as droplets having a diameter of more than 10 microns.
Surfactants are characterized by a hydrophile-lipophile balance (HLB) number that describes the strength of the hydrophilicity to the lipophilicity of the surfactant. Anionic surfactants having a HLB number of 20 to 40 are preferably used, and function to form micelles at low concentrations and to act as nucleation sites for the latex particles. Once nucleation is complete, the surfactants can additionally provide charge stabilization to the growing latex particles. Preferably the anionic surfactants contain a sulfate or sulfonate group and a hydrophobic moiety and may be, for example, alkyl sulfates, alkyl ether sulfonates and sulfates, alkylaryl sulfonates, and sulfosuccinates. Preferred anionic surfactants are the amine salt of dodecyl benzene sulfonic acid, salts of dioctyl sulfosuccinate, salts of lauryl sulfate, and salts of the ethoxylated alcohol half ester of sulfosuccinic acid. Exemplary alkyl and alkene sulfonates are described in U.S. Pat. Nos. 4,983,383 and 5,194,469.
Nonionic surfactants having HLB numbers of 5 to 35, e.g. 5 to 30, preferably 10 to 15, can also be employed. These surfactants lower the interfacial tension between the monomer oil droplets and the aqueous phase, and provide stabilization of the polymer dispersion by partitioning at the interface of the aqueous phase and the polymer particles. Thus they reduce the polymer dispersion""s sensitivity to shear, temperature and the presence of electrolytes. The nonionic surfactants can be linear or branched ethoxylated alcohols, ethoxylated alkylphenols, or block copolymers of ethylene oxide and propylene oxide. Preferably they contain 3 to 40 ethylene oxide repeat units and a hydrophobic moiety which may be a linear or branched C11-C15 secondary alcohol, nonylphenol or octylphenol, or are block copolymers of ethylene oxide and propylene oxide.
The amount of surfactant present is preferably such that high energy homogenization of the monomer component is not needed to form the latex. When little or no cosolvent is used, preferably a relatively large amount of surfactant (e.g. at least 5% based on the monomer component) is used so that the monomer component is dispersed in the reaction mixture as droplets having a diameter greater than 10 microns.
The amount of surfactant and cosolvent in the reaction mixture is preferably such that the units derived from the second hydrophobic monomer (if present) and/or the hydrophilic monomer are substantially randomly dispersed in the polymer.
The surfactant can be a polymerizable component which is incorporated into the polymer.
The choice of the surfactant may be influenced by the end use of the dispersion. For example, particularly useful surfactants for compositions used for coating corn seeds are fluorine-containing surfactants.
4. Cosolvents
The reaction medium preferably contains at least one cosolvent (also referred to as a diffusion modifier) which increases the solubility of the hydrophobic monomer in the reaction medium. It is generally present in amount at least 10% but less than 30%, preferably 5 to 20%, based on the water. Because the cosolvent increases the water solubility of the hydrophobic monomer, it increases the transport rate of the hydrophobic monomer from the monomer micelles or oil droplets to polymer nucleation sites. The cosolvents are preferably linear or branched monoalkanols containing 1 to 4 carbons, alkyl esters or alkyl ethers containing 1 to 6 carbons. Preferred cosolvents have a solubility in water of more than 0.7% at 25xc2x0 C. and have boiling points of 60xc2x0 to 130xc2x0 C., preferably less than 95xc2x0 C., so that they can be easily removed after the polymerization reaction. Preferred cosolvents include ethanol, isopropanol, ethyl acetate, n-propanol, sec-butanol, and t-butanol, and combinations thereof. Preferably the cosolvent has a water-octanol partition coefficient of at least 0.2 to enhance the solubility of the hydrophobic monomers in the water (see xe2x80x9cHandbook of Property Estimation Methods,xe2x80x9d edited by W. J. Lyman, W. F. Reehl, D. H. Rosenblatt, American Chemical Society, Washington, D.C. 1990).
The amount of cosolvent preferably used depends upon the amount and type of surfactant used. For example, where there is about 1.6% of ionic and non-ionic surfactants, at least 5% of the cosolvent is generally required to obtain a single sharp melting point crystalline polymer, whereas when about 0.8% of ionic and non-ionic surfactants is present, at least about 10% of the cosolvent is generally required.
5. Initiators
A free radical initiator must generally be present to cause the polymerization to take place, generally in amount 0.1 to 0.4% based on the reaction mixture. Alternatively or additionally, ultraviolet radiation can be used to initiate the reaction.
Initiators useful in emulsion polymerization are well known [see, for example, U.S. Pat. No. 5,516,865 and xe2x80x9cEmulsion Polymerization,xe2x80x9d Blackley (1975), chapter 6, Applied Science Publishers, London]. Suitable hydrophobic initiators for this invention include benzoyl peroxide and di-t-butyl peroxide. Suitable hydrophilic initiators include hydrogen peroxide and potassium and ammonium persulfate. A redox initiator, e.g. t-butyl hydroperoxide/ascorbic acid, or hydrogen peroxide/ferrous compound, can also be used.
6. Other Additives
The reaction mixture can contain a variety of other additives, including pH adjusters (e.g. sodium hydroxide and ammonium hydroxide); pH buffers (e.g. sodium bicarbonate and sodium hydrogen phosphate); coalescing agents (e.g. N-methylpyrrolidone, poly(ethylene glycol) alkyl ethers and poly(ethylene glycol); colloidal stabilizers (e.g. hydroxyethyl cellulose, polyacrylates and polyvinyl alcohols); rheology modifiers (e.g. hydroxyethyl cellulose and the products available under the trade names Kelzan and VCAR from Kelco and Union Carbide, respectively); and defoamers (e.g. the products available under the trade names Surfynol and Anti-foam H-10 Emulsion from Air Products and Dow Corning, respectively. The addition of sodium bicarbonate tends to increase particle size.
B. Polymerization Conditions
1. Single Stage Polymerization
The polymerization is generally carried out at 45 to 90xc2x0 C., preferably 60 to 80xc2x0 C. Lower temperatures decrease the amount of coagulum and increase particle size uniformity. Preferably the reaction is carried out under oxygen-free conditions, e.g. under nitrogen. Polymerization is preferably continued until at least 99% of the monomer component has been polymerized. Typically this takes 1 to 4 hours at about 70xc2x0 C.
The polymerization is preferably carried out under conditions such that the polymer is obtained in the form of particles having an average size of less than 1 micron, preferably less than 0.5 micron, particularly 0.25 to 0.35 micron (measured by the well known light scattering technique). Small particle sizes are desirable because the dispersions are more stable, and do not clog spray nozzles. Preferably the amount of monomer is such that the reaction product has a solids content of at least 25%, particularly at least 30%, especially at least 35%. Higher solids content is desirable because less water needs to be evaporated to form a coating, and because the product is less expensive to package and transport. However, the solids content is generally no more than 45%, because of the tendency of very high solids content dispersions to coagulate spontaneously.
After the polymerization is complete, the cosolvent, if used, is generally removed. At this stage, further additives can be added to the latex, depending on the intended use of the product.
2. Two Stage Polymerization
In some applications it can be desirable in a first stage to polymerize the hydrophobic component thereby forming a crystalline copolymer or homopolymer, and then polymerizing the hydrophilic component in a second stage. This results in phase-separated particles having a core of predominantly (at least 50% by weight) crystalline polymer and a shell around the core, the shell being formed predominantly of non-crystalline polymer. Generally, the core is substantially all crystalline polymer as a first phase, and the shell is substantially all non-crystalline polymer as the shell. This is desirable when there is a need to change the properties of the crystalline polymer, such as tack, without changing the Tm. The monomers used to form the shell are not limited to hydrophilic materials, but can also be monomers such as styrene or butyl methacrylate.
For a core/shell product, Tm is substantially the same as the crystalline homopolymer formed from the first hydrophobic monomer.
As in the single stage polymerization, the final latex preferably has a solids content of at least 30% and a residual monomer content of less than 1%; and the surfactant likewise preferably is present in amount such that the latex particles have an average particle size of less than 0.1 micron, particularly less than 0.5 micron.
C. Use of the Dispersions
The dispersions can be used to provide coatings on any solid substrate, e.g. fibers, seeds, or a shaped object. They can be applied to the substrate by means of conventional coating techniques such as wire-wound rod, direct gravure, offset gravure, reverse roll, air-knife, trailing blade coating, and spray coating. The coating is typically dried at a temperature at least 5xc2x0 C. above Tm of the crystalline polymer, under ambient conditions or by the application of heat.
1. Coating of Fibrous Materials
Compositions for treating fibrous materials preferably (a) contain 2 to 50% by weight of the particles comprising the crystalline polymer, and/or (b) contain substantially no organic solvents, and/or (c) contain less than 1% by weight of residual monomer. Preferably the composition is a latex prepared as described above, and for many purposes the polymer has a Tm of 20xc2x0 to 60xc2x0 C., particularly 40xc2x0 to 60xc2x0 C.
The composition can, for example, be dispensed from a pressurized container, or from a pump spray, or applied by means of a pad. The compositions can be used in place of starch, in which case the crystalline polymer has a Tm usually from 40 to 60xc2x0 C., which enables the polymer to be reset with an iron, but does not result in the polymer becoming reset in a clothes dryer. Alternatively, the polymer can give the fabric a xe2x80x9cpermanent pressxe2x80x9d character, by choosing a polymer having a Tm sufficiently high that it does not easily reset, e.g. at least 60xc2x0 C., preferably at least 80xc2x0 C. A similar result can be achieved by crosslinking the crystalline polymer after the fabric has been coated, e.g. by using an external crosslinker.
Compositions for treating fabrics preferably include an effective amount of at least one fabric-treating additive, this term being used to denote any compound conventionally used to affect the properties of a fabric. The amount of each such additive is preferably at least 0.1% by weight of the composition. Suitable additives include perfumes, scents, stain resisters, optical brighteners, wetting agents, preservatives, softeners, ironing aids (typically 0.05 to 1.5% by weight of a silicone, e.g. dimethyl or methylphenyl silicone or an amine-modified silicone), anti-static agents, and bleaching agents (e.g. as described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4th edition, John Wiley and Sons, volume 4, pages 271 et seq., and 552 et seq.). The composition can also contain a stabilizer, e.g. a naturally-occurring starch derived from corn, rice, wheat, or tapioca, or a modified starch, or carboxymethyl cellulose or a clay can also be employed.
Compositions for treating hair (particularly human hair, but also hair on a wig, or hair on a doll) preferably include an effective amount of at least one hair care additive, this term being used to denote any compound conventionally used in hair treating formulations. The amount of each such additive is preferably 0.01 to 10%, preferably 0.05 to 5%, based on the composition. Suitable additives include sequestering agents, hair-conditioning agents (e.g. cetyl trimethyl ammonium chloride, glyceryl monostearate, glycerin, propylene, glycol, sorbitol, urea, isopropyl myristate, balsam, lanolin, spermaceti, and isopropyl palmitate), anti-dandruff agents (e.g. sulfur, salicylic acid, resorcinol, bithionol, chloral hydrate, and zinc pyrithone), reducing agents (e.g. thioglycolates), bleaching agents (e.g. hydrogen peroxide, and perborate and persulfate salts), scents, perfumes, pearlescent aids (e.g. ethylene glycol distearate), preservatives (e.g. benzyl alcohol, methylparaben, propylparaben, imidazolidinyl urea, and esters of p-hydroxybenzoic acid), thickeners (also known as viscosity modifiers, e.g. methyl cellulose, starches and starch derivatives), coloring agents (e.g. any of the FDandC or DandC dyes), and pH adjusting agents (e.g. citric acid, sodium citrate, succinic acid, phosphoric acid, sodium hydroxide, and sodium carbonate). Other hair care additives are described in the xe2x80x9cCOSMETIC INGREDIENT DICTIONARYxe2x80x9d published by xe2x80x9cTHE COSMETIC TOILETRY AND FRAGRANCE ASSOCIATION INC.xe2x80x9d, U.S. Pat. No. 5,009,880, and Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol. 12, John Wiley and Sons, pages 881-917.
The pH of the hair-treating composition is typically 3 to 9, preferably from 6 to 7. For application to human hair on a person, Tm is preferably at least 40xc2x0 C. so that the hair does not become unset at high ambient temperatures, but generally is no more than 60xc2x0 C., so the hair can be reset with a hair dryer or curling iron. A particular advantage of the present invention is that the coatings can be applied to hair, and the hair can be repeatedly reset. Thus, the hair can be set in a desired configuration, and then by heating the crystalline polymer to a temperature greater than Tm, the hair can be reset into a second desired configuration. However, when the hair is on a wig or a doll, it can be desirable to set the hair more permanently. In such a case, Tm is sufficiently high, preferably at least 60xc2x0 C. Alternatively, or in addition, the composition can be externally crosslinked, as described above.
When a coating is formed on human hair, it is generally desirable that the coating can be easily removed by washing with water. This can be achieved by using a monomer component which contains (a) an XLC as described above, and/or (b) at least 0.5% of at least one amphoteric monomer, and/or (c) a carboxyl-containing monomer component as described above.
2. Coating of Seeds or Other Organisms
When seeds or other organisms are coated, the aqueous dispersion should be non-phytotoxic to the organism being coated. The dispersion is preferably applied by spray coating, the water then being evaporated by external heating or under ambient conditions. Other known application methods can be used. The thickness of the coating and the Tm of the polymer are preferably such that the coating is substantially impermeable to water at temperatures below Tm. Generally, the Tm of the polymer is from 0 to 40xc2x0 C., preferably 10 to 35xc2x0 C., and is equal to or greater than the lowest temperature at which the seed can germinate satisfactorily, and less than the highest temperature at which the seed can germinate satisfactorily. Preferably Tm is substantially equal to, or greater than, the optimum germination temperature of the seed. Minimum, optimum and maximum germination temperatures for different seeds are known to, or can be determined by, those skilled in the art (see, for example, Plant Propagation: Principles and Practice, by Hartman and Kester, 1959). At temperatures above Tm, the coating becomes substantially permeable to water. In this way, the coating prevents substantial imbibition of water by the seed at too low a temperature, thus preventing xe2x80x9cimbibitional chilling injuryxe2x80x9d and extending the dormancy of the seed, but permits the seed to imbibe water at temperatures at which germination can take place satisfactorily. It is not necessary for the coating to be completely impermeable to water at temperatures below Tm, and the term xe2x80x9csubstantially impermeablexe2x80x9d should be understood accordingly. For example, the coating preferably ensures that the seed imbibes no more than 21%, more preferably no more than 17%, particularly no more than 15%, especially no more than 10%, of water over a period of 48 hours at temperatures below Tm. Similarly, the coating need not be completely permeable to water above Tm and the term xe2x80x9csubstantially permeablexe2x80x9d should be understood accordingly. For example, the coating preferably has a permeability to water above Tm which is at least 2 times, particularly at least 3 times, its permeability below Tm. For example, at temperatures above Tm, the coating preferably permits the seed to imbibe. 25% or more, particularly 60% or more of water over a period of 48 hours at temperatures above Tm.
The permeability of the coating, as well as the value of Tm can be adjusted for the needs of the particular seed. For example, for corn seed, the coating preferably prevents the seed from imbibing more than 10% of water over a period of 48 hours below Tm, but permits the seed to imbibe more than 10% of water over a period of 48 hours above Tm. More than one coating can be applied to the seed.
The polymers used for coating seeds are preferably derived from a monomer component which includes a second hydrophobic monomer. Polymers which lack such a monomer tend to be difficult to apply, and to form tacky, relatively poor quality coatings. It is also preferred that the monomer component should contain a crosslinking component and that an external crosslinker should be employed. These measures result in a coating which maintains its integrity well below Tm, but which disintegrates easily when the seed expands, and which does not, therefore, interfere with germination and growth. Other measures which can be employed for the same purpose are the use of a monomer component which includes (a) at least 0.5% of at least one amphoteric monomer, and/or (b) a carboxyl-containing monomer component.
Although the foregoing description is directed principally to coating seeds for controlling the dormancy of the seed, the invention is useful for other organisms, and other purposes, e.g. to protect organisms from fungi and insects. Such other organisms include bacteria, embryos, eggs, sprouts, bugs, rhizobium, seedlings, and potato cuttings. Seeds which can be coated include vegetable seeds and grain seeds. For example, seeds for canola, maize, cotton, soybean, sugar beets, beans, tomato, potato, tobacco, corn, rice, wheat, sunflower, the brassica family, the solanaceae family, sorghum, barley, lentils, melons, cucumbers, cabbage, brussels sprouts, beans, and peas.
The composition applied to the organism can contain one or more additives, typically in amount 0.01 to 10%, preferably 0.05 to 5%, based on the composition. Suitable additives include colorants, fillers, soil pH adjusters, nutrients, seed protectors, phytotoxicity inhibitors, herbicides, growth regulators, soil improvers, fungicides, insecticides, growth stimulants, plant hormones, fertilizers, bird repellents, stimulants to accelerate growth, and innoculants. Such additives can alternatively or additionally be applied to the seed separately.